If your hearing aid has a telecoil, look for a phone with a high T rating. If it doesn’t, look for a high M rating. The auditory assistance devices are marked with the same ratings as cellphones. The best way to determine the sound quality you can expect from pairing the aid and cellphone is to add the two number ratings together. Try to achieve a combined rating of six, which is excellent. For normal, acceptable phone use, a combined rating of five will be sufficient, and a four indicates that pairing will only be acceptable for short calls.